1. Field of the Invention
The present invention relates to the filed of semiconductor processes and, more particularly, to a method of tantalum/tantalum nitride (Ta/TaN) deposition.
2. Description of the Prior Art
In the manufacture of silicon semiconductor devices, layers of barrier material are deposited to separate interconnecting metal from silicon and prevent their diffusion. As well known in the art, transition metal nitrides such as titanium nitride are widely used and examined as barrier materials in ultra-large scale integration of microelectronic devices between copper or aluminum and silicon.
Titanium nitride TiN has been the most studied barrier material and is used in production at current integration scale. However, titanium nitride has several limitations and will probably not meet future demanding requirements for device integrity, (i.e. device failure due to copper diffusion).
Tantalum nitride TaN has recently received extensive interest as a barrier material. Tantalum nitride provides superior physical properties with respect to titanium nitride. It has a high melting point, is very hard, highly conductive, and thermodynamically very stable with respect to Cu because it does not form copper-tantalum or copper-nitride compounds. As compared to TiN, the grain boundaries of TaN are often disordered while CVD-deposited TiN films typically exhibit a columnar grain structure. Due to this disordered grain boundary structure, TaN may prevent copper diffusion more efficiently than TiN.
Typical techniques used for deposition of TaN layers include physical vapor deposition (PVD), chemical vapor deposition (CVD) and atomic layer deposition (ALD). Reactive sputtering is the oldest technique, and it has been the main process for depositing tantalum nitride films. Sputtered films are usually quite free from impurities and have low resistivity, but the step coverage is poor.
Chemical vapor deposition (CVD) methods are a main technique currently used for deposition of TaN layers for different applications. The films made by CVD exhibit much better conformity than the films deposited by PVD methods. Conventional CVD processes, which rely on metal halides, required high temperature (for example, deposition of tantalum nitride from TaCl5 required 900° C.). This problem has been solved by using MOCVD precursors and low temperature plasma enhanced chemical vapor deposition (PECVD).The other variant of deposition process, atomic layer deposition (ALD) and its several enhancements, allows very good control of layer thickness and uniformity, provides a good step coverage, and relatively low deposition temperature. However, current approaches for forming TaN layers have low throughput and relatively high cost.
There is a constant need in this industry to provide a method of forming a TaN layer as barrier material in the fabrication of integrated circuits that is cost effective and has high throughput.